collection of computers connected to each other. it allows to communicate with each other and share...

Communication and

Open source concepts

Collection of computers connected to each other .

It allows to communicate with each other and share resources

and information.

Stand alone !!!

Network!!!

1. Sharing of peripheral devices : printers,scanners etc can be connected in a n/w.

2. Sharing of programs and data : less expensive to work with a same software by many employees

3. Better communications : email4. Security of information : files can be backed up or

duplicated on a device ,shared by others.5. Access to database : users can enter in to many public or

privately owned databases.

Advantages of n/w

1. If there comes a problem it ‘ll affect the entire network.2. Efficiency is depend upon the system manager.

Disadvantages

Distribution of s/w with its source code, its original instructions.

We can make improvements.Eg: linux, GNU

Controlled by FSF (Free s/w Foundation)


First computer n/w in the world

ARPANET : Advanced Research Projects Agency Network

Designed by ARPA for US Dept of Defence in late 1960’s

Evolution of n/w ing

Grandfather to the internet

NCP : N/w Control Protocol

NSF net :National Science Foundation n/w

ARPANET

Network of n/w sCommunication passible through : TCP/IPTransmission Control Protocol/Internet Protocol

Client Server architecture

Activities on the internet ?????

Internet

BSNL,MTNL,almost all the communication providers are ISP’s.

Internet Service Providers(ISP)

It is a client server s/w that permits multiple users to communicate online with real time audio,video and text chat in dynamic 3D environment.

Interspace

Reference to switching techniquesThree useful methods to establish communication link between a sender and a receiver.

They are 1. Circuit switching2. Message switching3. Packet switching

Ways of sending data across n/w

A dedicated physical path is established between source and destination.

Used in telephone conversationOnce this connection is established we can send messages .

Three phases : circuit establishment , data transfer and circuit disconnection

Circuit switching

1. Simple and require no special facilities2. Suitable for long continuous transmission3. Once connection is established data is transmitted with no

delay4. Full capacity of circuit is available for the users.

Advantages

1. Before data transfer , time required to establish a circuit

2. It is fully dedicated to the connected path, affect the n/w

3. Uneconomical for computers

Disadvantages

Message : logical unit of information and can be of any length.First append the destination address to the message.We have tow methods1. Store and forward : source to intermediate node ,inspect

for errors , transmitted to other node which is available and finally reach the destination.

Path taken by the node is dynamic.

Message switching

2. Broadcast method: message is broadcast over a common medium known as broadcast channel.

All nodes cheek the dest address attached to it .finally reach the dest.

This method require that all nodes are connected to the n/w simultaneously.

Advantages : 1. Unlike circuit switching , no physical connection required b/n src and dest2. Uses the channels effectively because channels are used only when messages are transmitted.

Disadvantages 1. Each node must have sufficient storage to buffer messages.2. In store and forward time delay will be there3. Too slow for interactive real time applications

It routes message data on packet basis.Message is divided into fixed sized packets. Each packet is transmitted independently ,either store and forward or broadcast.

All packets are re-assembled into original message at destination node.

Packet : contains src & dest addr,ctrl info,mesg no,ackno and error checking bytes etc.

Packet switching

Advantages :1. Unlike messages, packets are of small and fixed size, storage

req is minimal2. Routing is done on packet basis transmission is very fast3. Suitable for computers , used in internet

Disadvantages :4. Reassembling is needed5. Time taken can’t be predicted

Communication is the process of transferring messages from one point to another.We have three modes of data transfer1. Simplex : unidirectional flow of data2. Half duplex : one direction transmission at a time with

acknowledgement 3. Full duplex : simultaneous transmission in both direction

Data communication terminologies

Channel :path which helps in data transmission

Baud :number of signal changes per second.

1 baud = 1 signal change per sec = 1 bit per sec

Bandwidth :is the range or band or frequencies that a

transmission medium can carry in a given period of time.Expressed in hertz (Hz) or cycles per sec

The amount of data transferred per second.It is measured in bps(bits per second)

Data transfer rate

It carries signals over a communication path.Two ways1. Wired (telephone wire)2. Wireless

Wired communication

3. Twisted-pair wire4. Coaxial cable5. Fiber-optic cable

Transmission media

The telephone line.It consists of two strands of insulated copper wire , twisted around each other.

It is relatively slow. Does not protect well against electrical interference.

Twisted-pair wire

Advantages :1. It is simple2. Physically flexible3. Low weight4. Inexpensive

Disadvantages:

5. Repeaters are needed for long transmission6. Unsuitable for broadband, as it has low bandwidth

frequencies

Cable network (cable tv).

It consists of insulated copper wire wrapped in a solid metal shield and then in an external plastic cover.

Better than twisted as it resist noise.Faster transmission is possible.

Co-axial cable (co-ax)

Advantages :1. Data transmission is far better than twisted pair2. Used in cable n/w3. Can be used for broadband transmission

Disadvantages :

4. Expensive as compared to the previous5. Not compatible with twisted pair

Consists of hundreds of thin strands of glass or plastic that transmit pulsating beams of light rather than electricity.

Not affected by random electromagnetic interference in the environment.

Fiber-optic cable

Advantages :1. Much lower error rate 2. Lighter and more durable3. Transmission is more secure4. Used for broadband transmission

Disadvantages :

5. Installation problem6. Expensive7. Connection losses are common

1. Infrared transmission2. Broadcast radio3. Microwave radio4. Communication satellites

Wireless communication media

Sends data using IR waves at a low frequencyAdvantages :1. Used by TV remote control units2. Very secureDisadvantages :3. Unobstructed view must be there in b/n sender and

receiver4. Confined to short range

Infrared transmission (IR)

Tuning FM stationRequires a transmitter and a receiver (transceiver)

Advantages :

1. Provides mobility2. Cheaper than …3. Ease of communication

Disadvantages :4. Insecure 5. Affected by weather

Broadcast radio

Super high frequency radio waves

Used in satellite communication system

Advantages :1. Cheaper than …2. Communicate over oceans

Microwave radio

Disadvantages :1. Insecure 2. Strength may be reduced3. Affected by weather 4. High cost of design ,imple ,maintenance

These are microwave relay stations in orbit around the earth.Ground to satellite : up linkingSatellite to ground : down linking

Satellites occupy one of three zones1. GEO : Geostationary Earth Orbit : high orbit 2. MEO : Medium Earth Orbit : 5000-10000 miles up3. LEO : Low Earth Orbit : 200-1000 miles up

Communication satellites

Advantages :

1. Covers a large area2. Best for global coverage3. Commercially attractive

Disadvantages :

4. Technological limitations5. High investment cost

1. Modem (modemo)

Converts digital data in to analog and vice-versa for transmission.Modem modulates outgoing digital signals to analog signal for twisted pair and demodulates the incoming analog signal and converts it to a digital signal. ISDN :Integrated Services Digital Network.DSL : Digital Subscriber Line

Network devices

Registered Jack-45 : Standard type of connector for n/w cables.

Eight pins : For various configuration

RJ -11 :Used in telephone cables

RJ-45 Connector

One kind of n/w adapter.Supports for high speed network connections via cables.Also known as Network Interface Card (NIC)

Ethernet card (NIC)

Used in a wired n/w to connect Ethernet cables from a number

of devices together.

Simple device , require no configuration

Function included in other devices (modem & router)

Hubs aren’t used in n/w with only wireless connections.

Switches can be substituted in place of hubs

Hub

Device that joins multiple computers together within one Local Area Network(LAN)

It uses layer2 (Data link Layer ) of OSI model

Switch is generally more intelligent than hub.

Capable of inspecting data packets , determining the source and destination of each packet and forward it.Offers better performance than hub.

Switch

Hardware that acts as a bridge between two n/w s so that data can be transferred b/n number of computers.

It is a n/w point that acts as an entrance to another n/w.

Associated with router and switch ???Eg is a LAN connected to internet or other wide area n/w.

Gateway

n/w Topologies and types

Topology:

The logical layout or shape of a n/w is called a topology

We have1. Bus topology2. Ring topology3. Star topology4. Tree topology

Network Topologies and types

Like a bus system. (Bus & road)

All communication devices are connected to a common channel(road).

All nodes are connected to a single wire , the bus which has two end points.Info can be passed to another device through this bus

Bus topology

Advantages :1. Organized as client server or peer to peer n/w2. Simple and needs short cable length than ring3. Simple to install , older technology4. Easy to expand

Disadvantages :

5. Extra s/w needed to avoid collision6. If a connection is broken , entire n/w may stop working7. Slow8. Complex protocols are used

All communication devices are connected in a continuous loop

There are no end points

Messages are passed around the ring until they reach the destination

Ring topology

Advantages

1. Shorter cable length is needed as compared to star2. Each node is connected to other by using a single connection3. Messages flow in one direction , no scope for collision4. Fast and efficient5. Suitable to set up high speed n/w

Disadvantages :

1. If one system stop working entire n/w may stop2. Difficult to diagnose the fault3. Difficult to add remove or reconfigure new node

All computers and other communication devices are directly connected to a central server.

Messages are routed through the central hub to their destinations

Hub monitors the traffic

Start topology

Advantages :

1. Easy to install, hub prevents collision2. It needs one connection per node 3. Easy management of n/w4. Easy to detect faults5. Uses simple communication protocols6. Most popular used for LANs

Disadvantages :

1. Needs large quantity of cable2. Hub offers limited number of connection3. Working of n/w depends upon working of hub

Suitable for n/w having hierarchical flow of data.

Means data travels level by level

Tree topology

LAN (Local Area Network):

LAN connects n/w devices over a relatively short distance.eg :

school , home, office etc

Operating in a limited space, controlled and managed by a

single person.

Concepts of LAN , WAN and MAN

Advantages :

1. Can share devices like printer2. Workstations do not need their own hard disk or CD ROM

drives3. Save their work centrally on the n/w file server4. Communicate with each other5. One copy of application packages are needed.

Disadvantages :

1. Special security measures are needed to prevent unauthorized access

2. Need to be maintained by a skilled technician3. If server develops error all users are affected.

Spans a large physical distance.Internet is the largest WAN spanning the earthCollection of LANsRouter connects LANs to WANNot owned by one organizationUsed in ATMs

WAN (Wide Area Network)

Covers the area larger than LAN but smaller than WAN

Interconnection of n/w s in a city

MAN (Metropolitan Area N/w)